The present invention is directed to magnetic storage devices and, in particular, to a magnetic read/write head carriage assembly for data storage devices using a flexible, double-sided magnetic recording medium.
Early magnetic storage devices for data processing systems made use of contact recording. This recording method was superceded to some extent after development of a magnetic head loading assembly in which the head was spaced away from the magnetic surface even during recording operations. This latter arrangement, which is currently used in high speed magnetic "hard disk" storage systems, permits the magnetic head to "fly" on a thin air layer over the recording medium so as to permit intimate interaction between the transducer and the magnetic surface. Contact recording has been used continuously, on the other hand, for less expensive, low speed magnetic storage devices such as magnetic tape and, more recently, floppy disk recording systems.
As is well known, a floppy disk is a rotatable, flexible magnetic disk, normally arranged in a cardboard dust cover. The so-called "floppy disk drive"--namely, a device for reading and recording information on such floppy disks--have come into widespread use for program and data storage because of their relatively low cost and small size notwithstanding a relatively rapid access to recorded information.
In the original floppy disk systems, the transducer structure generally comprised a single magnetic read/write head having a contact surface formed as a segment of a spheroid, or at least in a curved shape. The transducer was mounted on a movable carriage or base so that it could be accessed to different circumferential tracks on a floppy disk. On the opposite side of the disk, and also in contact with the disk was a pressure pad mounted on one end of a spring loaded arm. This arm, which was pivoted at its other end to the carriage base, was controlled by a solenoid to move into and out of contact with the floppy disk to permit data transfer operations to take place. The purpose of the pressure pad was to exert a tracking force through the floppy disk against the single transducer.
Recently, however, floppy disk drives have been developed for floppy disks on which both sides are used for data storage and transfer operations: the so-called "double-sided" floppy disks. With these drives, a single low speed accessing mechanism continues to be employed but the storage capacity of the device is twice the capacity of a floppy disk drive using single-sided floppy disks. With these improved drives, the magnetic heads are arranged on opposite sides of the floppy disk in a generally opposed relationship, with only a slight offset in the two head gaps to avoid flux interaction.
As mentioned above, floppy disk drives have found widespread use in a variety of applications due to their low cost. Therefore, it has been the main objective in the design of these devices more than with other types of data storage devices, to achieve simple structures of high reliability.
Present floppy disk drive manufacturers are using two approaches in the design of read/write magnetic head carriage assemblies for contact recording operations on double-sided floppy disks. One of these approaches is known from the U.S. Pat. Nos. 3,946,439 and 4,089,029, both to Castrodale et al. With this type of magnetic recording device in which a pair of transducers contact opposite faces of the recording medium, each of the transducers is mounted on a relatively weak gimbal spring. Relatively rigid load arms bear on dimples located on the center of the transducers to form universal joint connections with the transducers. The load arms are mounted on relatively stiff gimbal spring portions and are independently biased toward each other to apply a predetermined force to the transducers. This known structure allows the transducers to pitch and throw with wobbling movements of the floppy disk and permits the arms to move together to find the location for the transducers which permits the floppy disk to remain planar. This arrangement is an effective solution in respect to accessing times and storage capacity; however, it is expensive and sensitive to adjustment.
Another magnetic recording device for double-sided floppy disks is described in U.S. Pat. No. 4,151,573 to Tandon et al. This device uses a fixed transducer on one side of the floppy disk and a movable transducer on the opposite side. The movable transducer is gimballed on a pivoted, spring loaded arm of low mass and high stiffness and urges the floppy disk against the fixed transducer with a light force. The force is adequate to correct the deflections of the recording surface in a direction normal thereto, although this arrangement requires a slight penetration of the fixed transducer into the plane of the floppy disk. The read/write head assembly described in this patent is extremely reliable and less expensive than the arrangement taught by Castrodale et al.; however, it exhibits a lower data transfer rate than the aforementioned arrangement for reasons which are not completely understood.